Catalytic alkylation of isobutane is well known in the art, being the union of an olefin with isobutane in the presence of an acid catalyst to produce high octane branched chain hydrocarbons (alkylate) for use in aviation gasoline and motor fuel. Specifically, the olefin is combined with isobutane in the presence of an acid catalyst in a reactor and undergoes an exothermic reaction. The acid is then separated from the reactor effluent. After acid separation, the reactor effluent proceeds to a series of distillation columns to separate the inert alkanes, the unreacted isobutane for recycle, and to recover the alkylate. Treating is also performed on some of the effluent to remove residual acid and undesired reaction products. A variation of this process has been to use the vaporization of a portion of the reactor effluent to cool the reactor, see Hydrocarbon Processing, September, 1974, page 206.
The vapors produced by cooling the reactor have been used to supply heat to a deisobutanizer distillation column. U.S. Pat. Nos. 3,162,694 and Re 26.060 disclose such a process. These processes however, suffer from several disadvantages.
First, the amount of vapors produced by cooling the reactor are normally not sufficient to supply the total heat necessary to the deisobutanizer. Secondly, the normally high operating pressures of the distillation columns makes it difficult to use these vapors as a source of heat.
The present invention solves the disadvantages of the existing art by using the reactor effluent to cool the overhead vapor streams of the distillation columns found in the process. This allows the distillation columns to operate at a much lower pressure. The increased vapors of the reactor effluent produced by cooling the distillation column overheads, along with the lower operating pressure of these columns, allows the total energy input to the process to be greatly reduced.